1/(x^2+7x)-1/(x^2+7x+6)+1/(x^2+7x+18)-1/(x^2+7x+12)=0
问题描述：
1/(x^2+7x)-1/(x^2+7x+6)+1/(x^2+7x+18)-1/(x^2+7x+12)=0
答
设y=x^2+7x+6原方程化为1/(y-6)-1/y+1/(y+12)-1/(y+6)=012/(y^2-36)-12/(y^2+12y)=01/(y^2-36)=1/(y^2+12y)y^2-36=y^2+12y12y=-36y=-3x^2+7x+6=-3x^2+7x+9=0x=-7/2±1/2√13经检验x=-7/2±1/2√13是原方程的解...